The present invention generally relates to an apparatus and a method for operating and etch chamber with reduced contamination and more particularly, relates to an apparatus and a method for preventing residual etchant gas in the middle chamber of an etch chamber from attacking metal sidewalls of the middle chamber by providing a bypass exhaust conduit to evacuate any residual etchant gas.
In the fabrication of semiconductor devices, particularly in the fabrication of submicron scale semiconductor devices, profiles obtained in etching process are very important. A careful control of a surface etch process is therefore necessary to ensure directional etching. In conducting an etching process, when an etch rate is considerably higher in one direction than in the other directions, the process is called anisotropic. A reactive ion etching (RIE) process assisted by plasma is frequently used in an anisotropic etching of various material layers on top of semiconductor substrate. In plasma enhanced etching processes, the etch rate of a semiconductor material is frequently larger than the sum of the individual etch rates for ion sputtering and individual etching due to a synergy in which chemical etching is enhanced by ion bombardment.
To avoid subjecting a semiconductor waiver to high-energy ion bombardment, the wafer may also be placed downstream from the plasma and outside the discharge area. Downstream plasma reactors etches more in an isotropic manner since there are no ions to induce directional etching. The downstream reactors are frequently used for removing resist or other layers of material where patterning is not critical. In a downstream reactor, radio frequency may be used to generate long-lived active species for transporting to a wafer surface relocated remote from the plasma. Temperature control problems and radiation damage are therefore significantly reduced in a downstream reactor. Furthermore, the wafer holder can be heated to a precise temperature to increase the chemical reaction rate, independent of the plasma.
In a downstream reactor, an electrostatic wafer holding device known as an electrostatic chuck is frequently used. The electrostatic chuck attracts and holds a wafer positioned on top electrostatically. The electrostatic chuck method for holding a wafer is highly desirable in the vacuum handling and processing of wafers. An electrostatic chuck device can hold and move wafers with a force equivalent to several tens of Torr pressure, in contrast to a conventional method of holding wafers by a mechanical clamping method.
Referring initially to FIG. 1, wherein a conventional inductively coupled plasma etched chamber 10 is shown. In the etch chamber 10, which typically represents one that is commercially available as a LAM TCP etcher, the plasma source is a transformer-coupled source that generates a high density, low pressure plasma away from a wafer surface. The plasma source allows an independent control of ion flux and ion energy. The plasma can be generated by a flat spiral coil (not shown), i.e. an inductive coil separated from the plasma by a dielectric plate 12 which is normally fabricated of a ceramic material with a gas inlet 14 provided therein. The ceramic plate 12 may be a dielectric window made of a substantially transparent material such as quartz to facilitate visual observation of the middle chamber 20. The middle chamber 20 is further formed by a bottom ceramic plate 16 equipped with an apertured opening 18 for allowing a plasma to pass thereto. The sidewall 22 of the middle chamber 20 is normally formed of a metallic material, such as aluminum, with an anodized aluminum surface. The top ceramic plate 12, the bottom ceramic plate 16 and the metallic sidewall 22 form a self-contained chamber, i.e. the middle chamber 20 which has a first cavity 24 therein.
A wafer 30 is positioned on the electrostatic chuck (or ESC) 26 sufficiently away from the RF coil (not shown) such that it is not affected by the electromagnetic field generated by the RF coil. A typical LAM TCP plasma etcher enables a high density plasma to be produced and a high etch rate to be achieved. In the plasma etcher 10, an inductive supply and a bias supply are further used to generate the necessary plasma field. In a typical inductively coupled RF plasma etcher 10, shown in FIG. 1, a source frequency of 13.5 MHZ and a substrate bias frequency of 13.5 MHZ are utilized such that ion density of about 0.5xcx9c2.0xc3x971012 cm3 is obtained at the wafer level, while electron temperature of 3.5xcx9c6.0 eV and a chamber pressure of 1xcx9c25 mTorr are achieved.
In the plasma chamber 10, after the wafer 30 is etched in the main chamber 32, the chamber is normally evacuated of the etchant gas from the middle chamber 20 and from the main chamber 32 by a turbo pump 34 controlled by a gate valve 36. The turbo pump is further connected to a dry pump 38 through a control valve 42. When the pressure in the chamber is too high, in order not to damage the turbo pump 34, control valve 42 closes while control valve 44 opens to allow the chamber to be evacuated by the dry pump 38 directly. Simultaneous with the pumping process, an inert purge gas such as nitrogen is flown into the middle chamber 20 and the main chamber 32 through gas inlet 14 to further facilitate the removal of residual etchant gas.
In the conventional plasma chamber 10, a problem caused by the residual etchant gas left in the cavity 24 of the middle chamber 20 frequently occurs. The residual etchant gas cannot be evacuated from cavity 24 due to the small holes in the apertured opening 18 situated in the bottom ceramic plate 16. The small holes do not allow a fast flow rate so that the evacuation of the middle chamber 20 is ineffective. The residual etchant gas left in cavity 24 attacks the metal sidewall 22 and thus causing corrosion in the metal. The corrosion of metal, for instance of an aluminum surface, produces particles which contribute to a severe contamination problem for the main chamber 32 where a wafer is positioned.
It is therefore an object of the present invention to provide a plasma etch chamber that does not have the drawbacks or shortcomings of a conventional plasma etch chamber.
It is another object of the present invention to provide a plasma etch chamber that is equipped with a middle chamber that has significantly reduced particle contamination problem.
It is a further object of the present invention to provide a plasma etch chamber that is equipped with a middle chamber and a main chamber which has significantly reduced contamination problem by evacuating residual etchant gas from the middle chamber.
It is another further object of the present invention to provide a plasma etch chamber that is equipped with a middle chamber for feeding an etchant gas plasma into a main chamber that has significantly reduced particle contamination problem.
It is still another object of the present invention to provide a plasma etch chamber that has a middle chamber and a main chamber equipped with a bypass exhaust conduit connecting the middle chamber to the main chamber.
It is yet another object of the present invention to provide a plasma etch chamber that has a middle chamber and a main chamber in fluid communication through an apertured opening and a bypass exhaust conduit.
It is still another further object of the present invention to provide a method for preventing corrosion in an etch chamber by residual etchant gas wherein the etch chamber is equipped with a middle chamber and a main chamber.
It is yet another further object of the present invention to provide a method for preventing particle contamination in an etch chamber by providing a bypass exhaust conduit connecting between a middle chamber and a main chamber such that residual etchant gas can be evacuated from the middle chamber.
In accordance with the present invention, an apparatus and a method for preventing particle contamination in an etch chamber are provided.
In a preferred embodiment, a plasma etch chamber is provided which includes a main chamber that has a first cavity, a wafer platform and a spent etchant gas outlet in fluid communication with a pump means for exhausting a spent etchant gas; a middle chamber that has a second cavity therein situated inside the first cavity and suspended over the wafer platform; the middle chamber is formed by a top ceramic plate, a bottom ceramic plate and a metal sidewall; the second cavity is in fluid communication with the first cavity through an apertured opening situated in the bottom ceramic plate for feeding an exhaust gas plasma into the first cavity; the second cavity is in fluid communication with an etchant gas source through an etchant gas inlet situated in the top ceramic plate; and a bypass exhaust conduit providing fluid communication between the second cavity in the middle chamber through an opening in the top ceramic plate and the first cavity in the main chamber such that any residual etchant gas in the second cavity is evacuated by the pump means through the first cavity without causing corrosion in the metal sidewall of the middle chamber.
In the plasma etched chamber, the main chamber may have a volume that is at least twice the volume of the second cavity in the middle chamber. The wafer platform may be an electrostatic chuck. The apertured opening in the bottom ceramic plate may be a shower head for dispersing an etchant gas plasma into the first cavity of the main chamber. The bypass exhaust conduit allows the residual etchant gas to flow therethrough at a flow rate at least twice the flow rate of the residual etchant gas flown through the apertured opening in the bottom ceramic plate. The spent etchant gas outlet may be in fluid communication with a turbo pump, or maybe in fluid communication through a gate valve for controlling a passageway of the spent etchant gas, the top ceramic plate and the bottom ceramic plate may be formed of a ceramic material that is resistant to the etchant gas plasma. The metal sidewalls of the middle chamber may be formed of aluminum. The etchant gas plasma may be formed of at least one member selected from the group consisting of Cl2 or BCl3 in the middle chamber by a radio frequency coil.
The present invention is further directed to a method for preventing corrosion in an etch chamber by residual etchant gas which can be carried out by the operating steps of first providing an etch chamber that includes a main chamber and a middle chamber, the main chamber further includes a first cavity and a wafer platform with the middle chamber suspended over the wafer platform, the middle chamber further includes a top ceramic plate that has an etchant gas inlet therethrough, a bottom ceramic plate that has an apertured opening for passing an etchant gas plasma therethrough and metal sidewalls defining a second cavity; connecting a bypass exhaust conduit between the first cavity in the main chamber and the second cavity in the middle chamber for providing an unrestricted flow of residual etchant gas from the second cavity after an etching process; conducting an etching process on a wafer in the main chamber; and evacuating residual etchant gas from the second cavity through the apertured opening and the bypass exhaust conduit by a pump means.
The method for preventing corrosion in an etch chamber by residual etchant gas may further include the step of evacuating residual etchant gas from the second cavity by a turbo pump, or the step of mounting a gate valve between the second cavity and the pump means. The method may further include the step of providing the wafer platform in an electrostatic chuck, or the step of positioning a wafer on the wafer platform for carrying out an etching process. The method may further include the step of providing the apertured opening in a shower head for dispersing an etchant gas plasma into the first cavity for etching a wafer. The method may further include the step of evacuating more than half of the residual etchant gas from the second cavity through the bypass exhaust conduit. The method may further include the step of evacuating more than xc2xe of the residual etchant gas from the second cavity through the bypass exhaust conduit. The method may further include the step of providing the metal sidewall in aluminum, or the step of igniting the plasma in the etchant gas flown into the second cavity.